1. Field of the Invention
This invention relates to apparatuses which provide internal information of a specimen by measurement of propagation time of ultrasonic wave traveling through the specimen, and more particularly to an apparatus for detecting a defect within a wooden pole and displaying information of the defect in graphical form.
2. Description of the Prior Art
In a wooden pole, an internal defect, such as rotten part which cannot be seen from outside may develop sometimes as years pass. In order to detect such a defect, various means have been developed, for example, means for boring a hole in a wooden pole by a drill as disclosed in Japanese utility model, publication No. 53-72580, and means for driving a probe into a wooden pole as disclosed in Japanese utility model, publication No. 53-79091. These techniques have disadvantages in that holes must be made in the wooden pole in order to perform the inspection. Also in order to detect existence of a defect by means of ultrasonic wave, there is another means for transmitting ultrasonic wave in closed contact state to a wooden pole as disclosed in Japanese utility model publication No. 53-69287. By using this means existence of the defect may be detected, but it cannot provide defect information in quantative form.
In Japanese newspaper "Asahi" dated Feb. 14, 1983, technique is reported where inside of a pole, even growth rings can be investigated by the computer tomography using X-ray owing to significant technical progress in recent years. Since such a technique uses X-ray the measuring apparatus becomes of considerable size which make it unpracticable for inspecting the pole. In Monthly Report of Electric Communication Research Institute (Japan) No. 36-4 (1983), it is set forth that ultrasonic propagation time is measured on diameter of a wooden pole and on a position perpendicular to the projecting direction of ultrasonic wave thereby existence of a defect in the wooden pole is detected and further location or depth of the defect is provided.
It is known well that, as the frequency of an ultrasonic wave increases, rectilinearity of propagation of the wave through a body is increased and therefore the resolving power required to investigate internal state of the body is improved, while the amount of attenuation is also increased. Consequently, an apparatus using an ultrasonic wave in high frequency region is required to generate high output power which makes it uneconomical.
An apparatus, such as a wood tester WTD-II of Eisho Denshi K.K. or a concrete testing machine of Cho-onpa Kogyo K.K., may be commercially available, in which an ultrasonic wave of relatively low frequency (50 kHz-100 kHz) is used and relation between the delay time and length of known defect within a subject is previously determined by means of experiment, and on the basis of this relation length of the defect is presumed from data of the delay time actually measured.
Any of above-mentioned means in the prior art, however, cannot provide information which locates the defect within a body. It is often required in maintenance concerning a pole that the information of the defect be obtained and adequate time for repair or exchange is provided.